1. Field of the Invention
The present invention relates to a charging device for charging a capacitor unit that includes therein a plurality of capacitors connected in series, an image forming apparatus that includes the charging device, and a computer program product.
2. Description of the Related Art
Recent capacitors have high capacity and excellent charge-discharge cycle characteristics, and therefore have been used in place of backup power supplies for electronic devices, auxiliary power supplies for image forming apparatuses, and batteries for motor vehicles and other various transportation devices. Furthermore, from the standpoint of the effective utilization of energy, the use of capacitors for storing nighttime power has been considered.
In the case of charging a capacitor unit that has therein a plurality of capacitors connected in series, it is commonly known that to charge the capacitors efficiently, when any of the capacitors has reached a predetermined charging voltage, the charging current for charging the capacitor is bypassed by a bypass circuit (a parallel monitor).
However, in the case of bypassing the charging current through the bypass circuit, there is a problem that loss of charging current occurs in the bypass circuit. To cope with this problem, there is disclosed a capacitor charging circuit capable of reducing power consumption in such a manner that when any one of the plurality of capacitors has reached a predetermined charging voltage and the charging current for charging the capacitor is bypassed by a bypass circuit, the charging current flowing into the capacitors is reduced, thereby suppressing power loss (for example, see Japanese Patent Application Laid-open No. 2005-253289).
However, the capacitor charging circuit disclosed in Japanese Patent Application Laid-open No. 2005-253289 has a problem that if the voltage balance among the capacitors is disrupted by the degradation of capacity due to the degradation of capacitors, self-discharge caused by being left without maintenance for a long time, or the like, even when one of the capacitors has reached the predetermined charging voltage, respective charging voltages of the other capacitors may be much lower than the charged voltage of the capacitor. In such a case, when a capacitor unit is charged with a reduced charging current, it takes a long time to charge the capacitor unit.